Membrane manufacture



United States Patent 3,133,889 MEMBRANE MANUFACTURE Jan F. A. Hazenberg, Pijnacker, and Borgert P. Knol, Haren, Netherlands, asslgnors, by mesne assignments, to American Machine 8: Foundry Company, a corporation of New Jersey No Drawing. Continuation 738,019, May 27, 1958. 1961, Ser. No. 139,886

Claims priority, application Netherlands June 3, 1957 29 Claims. (Cl. 260-24) Selective membranes have the property of being permeable to ions of positive (negative) sign and being not or less permeable to ions of negative (positive) sign. They are extensively used in electrodialysis processes and in general in processes for separating ions by means of an electric current passing through a series of chambers bordered by selective membranes. Such processes include the removal of mineral constituents from an aqueous solution such as desalting water, purification of industrial liquids such as sugar syrup, removal of salt constituents from milk and whey, hydrolyzing salts of weak acids or weak bases, double decomposition of salts. These membranes may also be used in measuring de vices such as potentiometers and the like.

One method of preparing such membranes is described in the British patent specification 778,001 according to which a sheet of an organic high-molecular hydrophobic material is chemically treated in such a manner that the resulting product contains ionic groups.

The starting materials known thus far for use in such a process show certain disadvantages. In many cases the products are rather brittle or at any rate mechanically not perfect; during the subsequent reactions necessary for introducing ionic groups complications may arise, etc.

The present invention is especially concerned with methods for obtaining a more satisfactory starting material for processes of such a type.

Although the invention will be described with respect to materials in sheet form it should be noted that in its broader aspects the invention also covers materials in other forms suitable for use in such processes as separating ions with the aid of an electric field, such as elecof application Ser. No. This application Sept. 22,

3,133,889 Patented May 19, 1964 branes, may be obtained by swelling a sheet, tube or the like of a poly alkylenic material such as polyethylene or polypropylene in a liquid aromatic vinylic monomer such as styrene or orthoand para-vinyl toluene and subject- 5 ing the swollen sheet or the like to a polymerizingtreatment.

An embodiment of the invention viz' a polyethylene sheet swollen in monomeric styrene will now be described by way of example.

It should be noted that data as to temperature, time, degree of swelling etc. are not invariable but depend more or less on the thickness of the sheet, the intrinsic viscosity of the polyethylene, etc.

The equilibrium during the swelling stage is soon reached. In a given case it was established that with a sheet of 100 microns thickness this equilibrium was reached within 15-20 minutes at 60 C.; if the sheet was kept longer in the monomeric styrene, no further swelling was observed. The temperature during the swelling stage is of influence especially with respect to the time required for complete swelling but it should be noted that the temperature is limited by the point at which the sheet completely dissolves in the styrene.

In the above-mentioned case the sheet took up 20-40 grams of styrene per 100 grams of polyethylene. This amount slightly depends on the thickness and the nature (intrinsic viscosity; manufacture history) of the polyethylene sheet. The same applies to the so-called polyethylene-extraction. Not only does swelling of the polyethylene in the styrene occur but also some of the polyethylene may dissolve away during the swelling stage. If a grams of polyethylene are swollen in styrene and then the styrene is removed by evaporation in vacuum at an elevated temperature (in Table I the results are given for keeping it 16 hours in vacuum at 80 (2.), the polyethylene sheet weighs b grams. The ratio a-bx 100 is called the polyethylene extraction; it amounts to about 0.2-3 percent. It should be observed that substantially all of the styrene is already removed long before 16 hours.

In Table I some results are recorded of the styrene absorption in a number of experiments. By the term absorption is meant that monomeric styrene which is taken up by the polyethylene in any way.

trodialysis processes, for instance materials in the form of tubes, beakers, plates, rods and the like.

This invention concerns: the manufacture of ion exchange material; ion exchange materials, particularly membranes, made by the process of the invention; and use of said materials for segregating ions in a fluid by contacting ion bearing fluid with materials made by he process of the invention. The invention includes a process for the production of ion exchange materials, particularly membranes, which comprises contacting a solid carrier polymer, such as polyethylene, and a vinyl aromatic monomer, such as styrene, until the liquid monomer is absorbed within the solid carrier polymer, polymerizing the monomer by thermal treatment above room temperature and below the softening temperature oi the carrier polymer in the presence of a free radical producing polymerization catalyst and thereafter introducing ion exchange groups into the composite polymeric product.

According to the invention an excellent starting material for use in processes by which ionic groups are introduced in the material, thus leading to selective mem- TABLE I Polyethylene Sweilln l Thlnk- Intrln- Dura- Ab- Pol Ab- Type nossln ste vls-tlon tn 'Damp.,sorptlon ethgsorpmloooslty mlnmoaslens or tlon corrons utes and traction recto s 100 1 10 no 100 1.10 00 40 21 1.0 1% 15-20 mg: 28F l 2. 1 80. l

I m dl EV 200 1.07 120 20 9.5 25 113! 300 1.07 10 15 2.4 17.4 200 1.07 20 so at 2.1 26.7 30 200 1.07 10-76 Film dlsso vs:

1' tat 1. 9b 00 60 I. 0 1. 8 0. 2 136 1.90 00 8. 8 1.8 10.1 135 1.96 00 50 9.0 9.0 11.0 135 1.95 00 17 0.0 22.6 136 1.96 00 Ellis: dlllflrrbl 65 Type of pol ethylene: Bstnnds tor hi hres Belgium); 8X7. idem British Via ugen QrQ a i pressure polyethylenut htlllp|-U.B.

lyethylene (Hideorltaln); 1' for low- For S and B.V. the intrinsic viscosity was determined in Decalin at 70 C.; for P in Tetralin at 120 C.

The absorption as measured is given as the amount of styrene in percent by weight calculated on polyethylene.

The polyethylene-extraction was determined as de scribed and is given in percent calculated on polyethylene.

The corrected absorption of styrene is the sum of the absorption of styrene as measured and the amount of extracted polyethylene and is given in percents calculated on polyethylene.

The variation in absorption was about one percent calculated on polyethylene. With a styrene-content of 25-30% this variation was consequently 6-7% calculated on the amount of styrene which was taken up. For an accurate determination of these values the sheet must be freed from adhering styrene e.g. with filter paper. In a technical process such a step of freeing from adhered styrene is not necessary although it may be desirable if an absolutely homogeneous membrane is to be obtained.

The styrene escapes very rapidly from the swollen sheet; after minutes scarcely any styrene was still present in the film.

This phenomenon calls for certain measures during the subsequent heat treatment for polymerization. Some of these suitable measures are heating in a confined space e.g. between glass plates, heating in a vessel saturated with styrene vapour, etc. Excellent results were obtained on a t cch .ica-l scale by heating in an aqueous saturated salt solution; this will be discussed below.

A polymerization catalyst may be dissolved in the monomeric styrene; examples are peroxides such as benzoyl peroxide and substances such as N,N-azo-bis-isobutyro nitrile.

The same applies to cross-linking agents such as divinyl benzene.

The polymerization temperature depends on factors such as:

The softening temperature of the swollen polyalkylene e.g. polyethylene; this factor sets an upper temperature limit;

The duration of the polymerization step; too low a temperature leads to a duration which is too long for a technical process;

The equilibrium of the swelling process which is the sooner established the higher the temperature.

Temperatures in the order of 60-110 C. are normal.

if the polymerization is carried out between glass plates dilficulties may arise if the sheet is to be removed after polymerization; these difilculties can be prevented by such measures as placing talcum powder on the glass plates before polymerizing the swollen sheet, dissolving zinc stearate in the styrene (for instance 0. l% by weight), placing zinc stearatc on the glass, covering the glass with cellophane and the like.

Heating the swollen sheet in water is not desirable, probably because some styrene dissolves in the water with the result that in the polymerized sheet less polystyrene is present than would correspond with the amount of monomeric styrene originally present in the swollen sheet.

Very good results are obtained, however when polymerizing by heating, with saturated solutions of electrolytes. Even with large amounts of polystyrene, the final sheets are of excellent quality and have a mechanical strength comparable to that of polyethylene itself. This is quite surprising because polystyrene is brittle, especially ll cross-linkages are present. The surface of the final sheets is smooth and the sheets remain opaque or even transparent.

As electrolytes diverse salts may be used such as sodium chloride, ammonium chloride, calcium chloride, sodium sulphate, ammonium lulphate, aluminium sulphate.

in Example 1 the polymerization step will be illustrated.

Example I Sheets of high-pressure polyethylene (thickness 100 microns) with an intrinsic viscosity (Decalin at 70 C.) of 1.10 were swollen in monomeric styrene at C. for 20 minutes. 2% by weight I f divinyl benzene and 1% by weight of benzoylperoxide were dissolved in monomeric styrene. The swollen sheets contained 30.1% by weight of styrene.

The swollen sheet was kept in an aqueous saturated solution of sodium sulphate at C. for 6 hours. Calculated on polyethylene the amount of polystyrene with various sheets was from 25 to 28%.

The conversion of such a sheet into membranes will be illustrated by Examples 2, 3 and 4.

Example 2 A sheet as prepared in Example 1 with a polystyrene content of 26.5% by weight calculated on polyethylene was kept in boiling chloromethyl mcthylether with tin tetrachloride as a catalyst for 4 hours. Determination of the chlorine content of the treated sheet indicated that there had been an almost quantitative reaction at the aromatic nuclei of the polystyrene component.

The sheet thus obtained was aminated by treating it with a solution of 25% of trimethyl amine in acetone at room temperature for 24 hours. Amination was almost quantitative as shown by nitrogen analysis.

The ohmic resistance of 1 sq. cm. of membrane thus prepared in 0.1 N sodium chloride solution in water at 20 C. was 4 ohms. The selectivity in l N/2 N potassium chloride in water was The capacity per gram of dry substance was 1.6 milliequivalents. The water content was 20% Example 3 A sheet as prepared in Example 1 with a polystyrene content of 26.5% by weight calculated on polyethylene was sulphonated by keeping it in a mixture of chlorosulphonic acid (75%) and carbon tetra chloride (25%) for 5 hours at room temperature. The membrane thus prepared had showed an ohmic resistance in 0.1 N NaCl of 9 ohms. if a mixture of 25% chlorosulphonic acid and 75% of carbon tetrachloride was used, the ohmic resistance was 11 ohms in 0.1 N NaCl.

In both cases the selectivity was good (82% in 1 N/2 N KCl); the capacity was 0.3 meq./g.

It is also possible to sulphonate with chlorosulphonic acid alone but this takes more time. After 18 hours an ohmic resistance of 8.5 ohms was found. In this case the membranes are generally somewhat more brittle than if the above-mentioned sulphonating mixture was used.

Example 4 A sheet with a thickness of 200 microns was swollen as described in styrene in which 4% by weight of divinyl benzene and 1% by weight of benzoyl peroxide were dissolved and then the swollen sheet was polymerized as indicated in Example 1. The polystyrene content was 25.2% by weight.

After having been kept for 9 hours in concentrated sulphuric acid (98.3%) at C. to which 4 g. HgCl, per litre of acid were added, the product was placed in H 50 and then in water. The ohmic resistance of the membrane was 2.8 ohms in 0.1 N NaCl; the selectivity in 1 N/2 N KCI was 72% and the water content was 44%.

Thinner sheets took less time (in the order of 1-2 hours) for the sulphonating step.

In order to show the influence of some reaction conditions some further experiments are recorded below.

The sheets were of styrcnized polyethylene of various thicknesses to 250 microns), various types of polyethylene (Sidnc-Belgium; Kalle-Germany; British Visqucen-Great Britain) were used according to Example 1 with varying amounts of divinyl benzene.

3,1ss,sss

Example 5 Styrenized polyethylene sheets (27% polystyrene) with a thickness of 250 microns and with 4% divinylbenzene dissolved in the monomeric styrene were treated with sulphuric acid of varying strength at a temperature of 100 C. The original polyethylene was from Sidac.

A. With addition of oleum (with S0,) 9. sulphuric acid with a strength corresponding to 100.4% was obtained. After a treatment of 30 minutes the ohmic resistance of the sheets was still very high (1600 ohms) after 35 minutes treatment sheets were obtained with an ohmic resistance of 7 ohms and having a good mechanical strength. After 50 minutes treatment the sheets showed an ohmic resistance of 3 ohms but the products became somewhat brittle.

B. With sulphuric acid of 98.5% it took 2% hours to obtain a membrane with an ohmic resistance of 7 ohms and a good mechanical strength.

C. With 95.6% sulphuric acid results were not satisfactory in this case.

Example 6 The product to be sulphonated was either identical to that of Example 5 or it was obtained by using 2% instead of 4% of divinylbenzene dissolved in the monomeric styrene. In the first case a good product was obtained (resistance 9 ohms) with H 80 98.3% at 100 C. after 2 hours; in the second case (2% divinyl benzene) it took about 2 hours of treatment with H 80 to reach an ohmic resistance of 5 ohms.

In general higher cross-linking means a somewhat longer sulphonation time.

Whereas with 95.6% sulphuric acid a product of the first type (4% divinyl benzene) could not be sulphonated satisfactorily, a product of the second type (2% divinyl benzene) gave a membrane with an ohmic resistance of about 5 ohms after 6 hours.

Experiments have been carried out with sulphuric acid containing a slight amount (in the order of 0.5% by weight) of silver nitrate.

This leads to considerable shorter sulphonating times than if no addition to the sulphuric acid was made and, moreover, the bath can be used for much longer times, always giving membri. -s of low ohmic resistance and good selectivity.

If the experiment mentioned in the last paragraph of Example 6 was repeated but with addition of 0.5% by weight of AgNO, to the sulphuric acid, after 1 hour a membrane with a resistance of 7 ohms was obtained, whereas after 1 hour in sulphuric acid without additives, in sulphuric acid of the same strength (95.6%) the ohmic resistance was much higher.

Comparison of some tests of sheets of the 4%-diviny1 benzene type and of the 2%-diviny1 benzene type showed that with sulphuric acid and 0.5% AgNO; after the same period of sulphonation the ohmic resistance of the membranes in the latter case is about half of that in the first case.

However, in the latter case the selectivity of the membranes in about 10-15% lower. The water content is somewhat higher.

These examples are given only to convey an idea of the influence of diverse factors. Slight variations will always be found, depending e.g. on the nature of the polyethylene used in the first stage and on the styrene content in the swollen sheet.

Not only polyethylene may be used but also polypropylene.

Compartive tests have been carried out by using Ziegler low pressure polyethylene, and two types of polypropylene viz. "Moplen 14/2," and "Moplen M/2," both from Montecatini (Italy). The melting point of "Moplen A/2" was 170-172 (2.; its chemical analysis 85.09% C, 14.24% H and 0.33% ash. The melting point of "Moplen M/2 was 167-169 (3.; its chemical analysis 84.85% C., 14.17% H and 0.54% ash.

Swelling the sheet in monomer styrene was done by keeping the sheet for 15 minutes in the styrene. Results are recorded in Table 11.

TABLE II Polyalkyleue Swelling Thlelr- Intrln Toma) Absorp- Poly- Absorp- Type ness rnlsic vls tion n1ea nliryiene tion corerons ooslty sured extraction rected In this Table II Z stands for Ziegler polyethylene and A/2 and M/2 for Montecatini polypropylene.

The intrinsic viscosity for Z was measured in tetralin at C.; for A/2 and M/2 in tetralin at C. The extraction was determined as indicated with respect to Table I.

In order to establish the polymerization conditions sheets of Ziegler polyethylene were swollen in styrene at 70 C. and 80 C. for 15 minutes (experiments 1, 2 and 3 and 4, 5 and 6); the styrene contained 1% by weight of ,benzoyl peroxide and 2% by weight of divinyl benzene. The Montecatini polypropylene was swollen (both A/2 and M/Z for 15 minutes at 80" C. in styrene containing 1% by weight of benzoyl peroxide and 0.5% by weight of divinyl benzene (experiments 7-12).

Polymerization was carried out by keeping the swollen sheets in a saturated aqueous solution of sodium sulphate at 70 C. for 6 hours.

The results are given in Table III.

TABLE I11 Type polyalkylsne No P P. B, 0

1 10.9 12.1 1s 80 2 10.9 12.1 16 B0 3 11.0 12.8 is 86 4 14.0 111.4 20.4 80 6 12.0 111.11 20.4 80 0 14.8 111.7 20.4 82 7 111.4 17.5 21.4 51 8 17.6 18.0 21.4 87 0 18.6 10.0 21.4 91 10 13. 0 20. 8 30.1 00 11 14.0 21.8 110.1 72 12 17.2 25.0 30.1 82

In this Table 2, A/2 and M/2 have the same meaning as in Table 11.

P is the increase (in percent) of the weight of the polymerized sheet as compared with the weight of the polyalkylene sheet used as a starting material. P is a value, obtained from P by adding to P the value of the polyalkylene extraction in percent calculated on polyalkylene; this term has been explained with reference to Table l. in experiments No. 1, 2 and 3 this percentage was 1.2 (see Table 11 for 2 at 70 C.); in experiments No. 4, 5 and 6 it was 2.4 (see Table II for 2 at 80 0.); in experiments No. 7, 8 and 9 it was 1.1 (see Table II for A/2 at 80' 0.); in experiments No. 10, 11 and 12 it was 7.8 (see Table II for M/2 at 80' 0.).

7 S is the value of the absorption corrected as listed in Table II for Z (70 (3.), Z (80 C.), A/2 (80 C.) and M/2 (80 C.).

O is the degree (in percent) to which polymerization has taken place with Not only with the polyalkylcnes recorded in Table 111 but also with other polyethylenes (e.g. high-pressure polyethylenes) O has always been found to be in the order of 80%; this means that of the monomeric styrene which was taken up during the swelling stage, 80% is polymerizcd (to polystyrene) in the final product.

Sulphonntion was carried out with the sheets No. 6, 8 and 11 of Table III in sulphuric acid (95.6%), to which 0.2% by weight of silver nitratc had been added. at a temperature of 100 C. The sheets are indicated as Z-6. A/2-8 and M/Z-ll respectively. In Table IV some results are given with respect to duration of sulphonation (time in hours), ohmic resistance of the membrane in 0.1 N NaCl, selectivity in l N/2 N KCl, water content in percent, sulphur analysis in percent and in milliequivalents.

TABLE IV Time Selec' Type .si -i1. III 02 The mechanical properties of the membranes in the wet state are always good; in a very dry state they tend to become somewhat brittle.

From the above-mentioned styrenizcd sheets (4, 9 and 12 of Table 111) also positive membranes have been prepared by chloromcthylating and aminating the sheets as indicated in Example 2. The chloromethylation took place with chloromethyl mcthylether +25% tintetrachloride. The temperature with the polyethylene (Ziegler) was 55 C., with the polypropylene (A/Z and M/2) it was 58-50' C. Aminating was effected in trimcthylamine (25%) plus water (75%) at C.

After 6 hours with polyethylene the chloromcthylation was at its maximum; for polypropylene the maximum was reached after 2 hours both for A/2 and M/2.

In Table V the results are given for the aminating step. Here it is the nitrogen content which is a measure of the degree of conversion and again (as in Table IV for the sulphur content) the results are given in percent and in milliequivalcnts. Ohmic resistance is again given in 0.1 N NaCl; selectivity in l N/2 N KCl as usual. The water content is in percent.

TABLE V '1" ps Duration Ohrnlo Soleetlv- N, polynilrylsno amtnntlon resist it 11 0 percent. meq.

111 hours once 4B 41' 90 12.3 1.47 1.05 24 9. 0 00 20. 0 1. 81 1. 20 (I 24 7. 0 03 88. B 2. 32 1. 00

Both the membranes on polyethylene base and those on polypropylene base had a good mechanical strength.

The positive membranes on a base of polypropylene were much less brittle in a very dry state than the negative membranes on a polypropylene base in a very dry state.

As indicated, chloromethylation can also be carried out by keeping the styrenized sheet in chloromethyl methylether vapour instead of in the liquid. In Table VI some results are given obtained with styrenized highpressure polyethylene (27% polystyrene; the monomeric styrene containing 2% divinylbenzcne). As catalysts were used tin tetrachloride (1.0 and 2.5 and 5.0% SnCl, calculated on the other chloromethyl methylether) and titanium tetrachloride (3.65% of which is equivalent to 5% Such). The chlorine-contcnt is a measure for the degree of conversion. Amination was carried out with aqueous trimethylamine (25% amine-+% H 0) for 24 hours at room temperature. Here again 14% and N meq. have been given as in Table V.

TABLE VI Time In Per- Resistance, N, N, Catalyst vapour cent ohms. 11 0 per moq.

In hours CI 0.1 N NuCl cent 1% 811Gb.-. 0.5 5.0 10.5 18.8 1.81 1.31 1 5.8 9.0 21.2 2.00 1.43 1.5 0.3 9.3 21.0 2.21 1.58 2 0. 5 9. 0 20. 7 2.18 I. 56 2.5% SnCh... 0.5 5.1 12.0 18.8 1.81 1.29 1 6.0 9.3 20.7 2.29 1.64 1.15 6.9 11.4 19.8 2.32 1.66 2 0. B 10.2 19.2 2.32 1.66 5% SnCh-..-. 0.5 7.6 18 15.9 2.19 1.50 1 B. 0 12 18. 1 2.28 1. 63 1.5 5.4 17.7 19.3 2.42 1.73 3.05% T1011.-. 3 2.8 44.8 15.0 1.37 0. 98 0 5.3 10.0 21.3 2.08 1.49

The selectivity (1 bill N Kcl) is good. With 1% SnCl and 0.5 hour chloromethylation, a selectivity of was obtained after amination.

Chloromethylation in vapour takes less time than in liquid. With 2.5% SnCL; after 6 hours a chlorine percentage of 5.0% was reached it. liquid; in vapour after 0.5 hour already a chlorine percentage of the same magnitude (5.1%) was found.

The mechanical properties of the membranes listed in Table VI were very good.

Also with "Moplen All" and M/2" experiments with chloromethylation in chloromethyl methyl ether vapour instead of liquid have been carried out but here no appreciable differences have been noted in comparison with the experiments recorded in Table V regarding the duration of the chloromcthylating step; this is probably due to the fact that in Table V chloromethylation in liquid with polypropylenes was completed already after 2 hours. whereas the chloromethylation of the Ziegler base product listed in Table V took about 4-6 hours in liquid ether. On the other hand it is also possible to chloromethylate a Ziegler base product in liquid phase within a short time.

Amination can be done not only with trimcthylamine but also with other amines. In Table VII some cases are recorded. The starting material was styrenized (sidac) polyethylene with P =31.7%. This value shows that it is easy to obtain highly styrenized products; the values listed in Table III are much lower, showing that there is no difiiculty to produce a wide range of polystyrene contents. During the previous swelling step in the monomeric styrene 2% by weight of divinyl benzene were dissolved. Chlororncthylation took place in C1 CH OCH, (liquid) with 5% SnCl for 1.5 hours at 55' C. Chlorine analysis 4.95% CI. The sign (7) means that no value was determined.

TABLE VII Tlmo Ohmic Seleettvlty, amlna- Amine resistance, lN/2N 1110, N, N,

0.1 N K01 Percent Percent meq. hours NuCl t as a at it. a i a at is lit iii a is i it; a at ta iii 1 1a. a an 18.1 1.30 0. 03 i 2:2 at is its 4 1 as 22.7 11.1 0.79 1 a. 3 so 23. a 1.10 0. 79 2 Pyridine (50%) water 0.0 80 26.7 1.04 0.74 3 i (50%). 4.1 (:3 28.3 1.18 0.84 t m t at at mo ynmnoe nl lmlliititilliit at a as a: iii

In some cases the nitrogen content given in Table VII This can be done by first introducing halogen atoms in is somewhat higher than could be expected. This is due the sheet e.g. by chloromethylation and then reacting to the difficulty of removing the non-converted amine with amines, pyridincs. guanidincs such as pentamcthylcompletely from the membrane. guanidine dissolved e.g. in acetone, with sodium amide The mechanical properties of the membranes were in liquid ammonia, with dimethylsulphide e.g. dissolved good to excellent. in benzylalcohol or acetone etc. In an analoguous way It is possible to use also other aminating liquids such phosphonium groups may be introduced. Sulphonation as pure dimethylaniline and pure triethylaminc but can be done with sulphuric acid, a mixture of sulphuric the ohmic resistance was found to be rather high for acid and sulphur trioxide, chlorosulphonic acid, etc. In practical purposes. With pure tricthylamine for instance an analoguous way phosphoric acid groups may be inat a temperature of 50 C. and 2 hours treatment a rctroduced. sistance of 26.0 ohms was found. In general the ionic groups must be of such a type that The sulphonated membranes can be improved considtheir dissociation constant is at least 10-; by the term erably by treating them with bleaching lye. In general dissociation constant of an ionic group" is meant the by this treatment their ohmic resistance is reduced to dissociation constant of the compound in which the ionic about half their initial value. Neither the composition group is attached to a lower alkyl group. The amount of the bleaching lye nor the temperature or the duration of ionic groups in a membrane is expressed in milliof the treatment are very critical. With a given sulphoequivalents per gram of dry membrane; for practical purnated membrane having an ohmic resistance of 12 ohms/ poses the value should exceed 0.15 meq./g. of dry memsq. cm. and a selectivity in 1 N/2 N KCl of 88 after a brane. treatment or 24 hours with bleaching lye (20% NaOH; Probably the products according to the invention con- 12% active chlorine) at room temperature an electric sist of an autonomous matrix of eg polystyrene loosely resistance of 6 ohms/cm. was found. In another case lying in the polyalkene. the resistance of a sulphonated membrane of 24 ohms The excellent mechanical properties of the membranes (which is rather high for practical purposes] could be (substantially equal to those of the polyalkylene) are reducedto 12 ohms by treating it for 3 hours at room ascribed to the polyalkylene component and the excellent temperature with bleaching lye (5% active chlorine). electrical and electrochemical properties are ascribed to Generally the capacity of themembrane is somewhat inthe fact that the ionic groups can be attached easily to creased by the treatment (by about 20%), the selectivity the aromatic component for instance to the polystyrene is somewhat decreasedt by about 20% component.

A great advantage or 1 thejproccss according to the The membranes combine the good properties of both invention isthat'not only negative membranes oflgood' initial components. The mechanical properties of e.g. quality "rna'y lae' obtained but also jpositivejriernbranes polystyrene are quite unsuitable for membranes and on with 5urpriingly, good g lgcfr icalland.mechanical propthe other hand the conversion of pure polyalkylenes 10 me r high is of gtcat practical importance, membranes is difficult to achieve; if for instance poly- Ifa cross-linking'agent suchas divinyl benzene is .used ethylene is sulphonated there is always a moment that 'in theswellin'g and in'thefpolymerizatingstage its tim 50 the polyethylene film swells enormously in the sulphonation' seems toibe-"thata'homogeneous film is' obtained which that remains homo'geneous after ionic groups have been introduced and that the membrane is'insoluble in water or electrolyte solutions. The content of cross-linking agent does not substantially influence the degree of polymerizationjbut it infiuenccsthe water content of the membranes} 7 v g The newJproducts area; very suitable starting material ,for: .the process, indicated in the. first v paragraphs namely introducing ionic groups in the organic high rnolecular omejof these processes have been described tion bath, at which moment thefilm is mechanically so hydrophobicfmaterial; andso forming selective mem- I weak that it can scarcely be handled. No such difficulties arise with the p. oducts according to the invention.

If monomeric styrene is used as a swelling agent it need not be chemically pure. Technical styrene and mixtures such as styrene and methylstyrene may be used as well and the term styrene should be understood to cover also these products.

. .This is a continuation of S.N. 738,019 filed May 27, 1958, now abandoned.

What is claimed is:

1. The process for the production of ion exchange membranes which comprises contacting a vinyl aromatic monomer'with a solidcarrier polymer until the'rnonomer is absorbed therein, polymerizing said monomer within said polymer by thermal treatment above room temperature and below the softening temperature of the carrier polymer in the presence of a free radical producing polymerization catalyst and thereafter introducing ion exchange groups into the polymerized monomer.

2. The process according to claim 1 wherein the carrier polymer is shaped into a film.,

3. The process according to claim 1 wherein polymerization occurs in a confined space.

4. The process according to claim 1 wherein the polymerization catalyst is selected from the group consisting of bcnzoyl peroxide and N,N-azo-bis-isobutyro nitrile.

5. ,The process according to claim 1 wherein the polymerized vinyl aromatic monomer is cross linked.

6. The process according to claim 5 wherein cross linking is conducted with divinyl benzene.

7. The process according to claim 1 wherein the carrier polymer is polyethylene and styrene is polymerized and sulfonated.

8. A process of converting a polyalkylene selected from the group consisting of polyethylene and polypropylene into a homogeneous ion exchange material comprising an autonomous continuous matrix of a polymerized vinyl aromatic compound containing chemically attached ionic groups supported within and crosslinkcd through said polyalkylene, said ionic groups being present in an amount of at least 0.15 milliequivalents per gram of dry substance and having a dissociation constant of at least which comprises the steps of swelling said polyalkylene with a liquid monomeric vinyl aromatic compound, polymerizing said swollen polyalkylene product containing said monomeric vinyl aromatic compound by heating above room temperature and below the softening temperature of the polyalltylene and thereafter attaching ionic groups to the product.

9. The process of claim 8 wherein a polymerization catalyst is dissolved in said monomeric vinyl aromatic compound.

10. The process of claim 8, wherein a cross-linking agent is dissolved in said monomeric vinyl aromatic compound.

11. A process of converting polyethylene into ion exchange'material consisting of an autonomous continuous matrix of polymerized styrene containing quaternary ammonium groups supported on and crosslinked through continuous polyethylene material, said quanernary ammonium groups being present in an amount of at least 0.15 milliequivalent pergram of dry substance and having a dissociation constant of at least 10*, which comprisesthe steps of swelling said polyethylene with liquid monomeric styrene, polymerizing said swollen polyethylene. containing monomeric styrene by heating to a temperature between 60 and 110' C. reacting the polymerized -styrenq eontained in the polyethylene matrix with chloromethyl methylether under chloromethylating conditions, and reactingthe polymerized chloromethylated styrene'contained in the polyethylene matrix with a tertiary nitrogen compound under quaternizing conditions to recover .said ion'exchange material.

12. The process of claim -11'wherein a cross-linking agent is dissolved insaid liquid monomeric styrene.

13. A process of converting polyethylene into ion exchange material consisting of an autonomous continuous matrix of polymerized styrene containing sult'o-groups supported on and crosslinked through polyethylene, said sulfogroups being present in an amount of at least 0.15 milliequivalcnts per gram of dry substance and having a dissociation constant of at least 10, which comprises the steps of swelling said polyethylene with liquid monomeric styrene, polymerizing said swollen polyethylene containing monomeric styrene by heating to a tempera ture between 60 and C. in reacting the polymerized styrene contained in the polyethylene matrix with a sulfonating. agent selected from the group consisting of chlorosulfonic acid, oleum and sulfuricacid at temperatures up to 100 C. and recovering said ion exchange materiaL.

14. The process of claim 13, wherein the sulfonation step is conducted with chlorosulfonic acid at room temperature.

15. The process of claim 13, wherein the sulfonation step is conducted with sulfuric acid at elevated temperatures.

16. The process of claim 15, wherein a silver nitrate catalyst is dissolved in the sulfuric acid.

17. The process of claim 13, wherein a cross-linking agent is dissolved in said liquid monomeric styrene.

18. In a process for the production of ion exchange material which comprises imbibing a liquid vinyl aromatic monomer within a solid carrier polymer and polymerizing said monomer within said polymer at a temperature above room temperature and below the softening temperature of the carrier polymer in the presence of a free radical generating catalyst to form a polymeric product, the step of the thereafter introducing ion exchange groups into said polymeric product.

19. A process according to claim 18 wherein the carrier polymer is polypropylene.

20. A process according to claim 18 wherein the carrier polymer is polyethylene.

21. A process according to claim 18 wherein the liquid monomer is styrene.

22. A process according to claim 18 wherein the liquid monomer is vinyl toluene.

23. A process according to claim 18 wherein the carrier polymer is formed into a shaped product.

24. A product made by the method of claim 1.

25. A product made by the method of claim 8.

26. A product made by the method of claim 11.

27. A product made bythe method of claim 13.

28. A product made by the method of claim 18.

29. The method of segregating ions in a fluid which comprises contacting said fluid with material made by the method of claim 18.

References Cited in the fileof this patent UNITED STATES PATENTS 2,834,746 Salyer May 13, 1958 2,837,496 Vandenberg lune 3, 1958, 2,965,697 Duddy Dec. 20, 1960 OTHER REFERENCES Chen et al.: J. Polymer Science, volume 23, pages 903- 913 (February 1957). 

1. THE PROCESS FOR THE PRODUCTION OF ION EXCHANGE MEMBRANES WHICH COMPRISES CONTACTING A VINYL AROMATIC MONOMER WITH A SOLID CARRIER POLYMER UNTIL THE MONOMER IS BSORBED THEREIN, POLYMERIZING SAID MONOMER WITHIN SAID POLYMER BY THERMAL TREATMENT ABOVE ROOM TEMPERATURE AND BELOW THE SOFTENING TEMPERATURE OF THE CARRIER POLYMER IN THE PRESENCE OF A REE RADICAL PRODUCING POLYMERIZATION CATALYST AND THEREAFTERR INTRODUCING ION EXCHANGE GROUPS INTO THE POLYMERIZED MONOMER. 